The following abbreviations are used herein:
TABLE 1ACKacknowledgementCAcarrier aggregationCIFcarrier indicator fieldCRScell-specific reference signalCSScommon search spaceDAIdownlink assignment indexDCIdownlink control informationDLdownlinkeIMTAenhanced interference management and trafficadaptationE-UTRAevolved universal terrestrial radio accessFDDfrequency division duplexH-ARQ or HARQhybrid automatic repeat requestH-ARQ ACKhybrid automatic repeat request acknowledgmentHetNetheterogeneous networkIEinformation elementLTElong term evolution(E)PDCCH(enhanced) physical downlink control channelPCellprimary component carrierPDSCHphysical downlink shared channel(E)PHICH(enhanced) physical H-ARQ indicator channelPUCCHphysical uplink control channelPUSCHphysical uplink shared channelRRCradio resource controlRTTround trip timeRel.Release (e.g. LTE Rel. 11 means LTE Release 11)SCellsecondary component carrierTDDtime division duplexUEuser equipmentULuplinkUL-SCHuplink shared channelUSSUE specific search space
E-UTRA supports both FDD and TDD duplex modes. While interworking mechanisms between E-UTRA FDD and TDD have been specified, the behaviour of terminals (e.g. UEs) which are simultaneously connected to the network on two (or more) bands with different duplex modes has not been specified. For network operators with both FDD and TDD spectrum, it would appear to be important to provide efficient mechanism(s) or means for allowing both spectrum resources to be well (preferably fully) utilized in order to improve system performance and user experience.
The use of carrier aggregation (CA) offers a means for increasing peak data rates and throughput, as has been discovered during Rel. 10 LTE CA work, and it has been enhanced during Rel. 11 LTE CA enhancement work.
Efficient TDD and FDD spectrum usage and utilization of different technologies jointly are becoming more and more important for future LTE deployments in order to accommodate increased throughput and capacity needs. There may therefore be an increased need to support joint LTE FDD-TDD operations such that both spectrum resources can be well or fully utilized to improve system performance. It is expected that, in future LTE FDD-TDD CA deployment scenarios, either a TDD or a FDD cell may be used as the primary component carrier (PCell), and therefore support for generic LTE FDD-TDD CA would appear to be needed.
As an important technology in CA systems, cross-carrier scheduling enables the PDSCH and PUSCH resource on one carrier component to be scheduled by PDCCH on another carrier component. For instance, PDCCH can be transmitted on one serving cell (e.g. a serving cell with better link quality) and the related PDSCH or PUSCH may be transmitted on another serving cell. This may be realized by adding a 3-bit carrier indicator field (CIF) in downlink control information (DCI) format. In the FDD-only or TDD-only CA systems in Rel. 10 and Rel. 11, the number of blind decodings remains the same regardless of whether or not cross-carrier scheduling is configured. In LTE FDD-TDD CA system with cross-carrier scheduling, however, the number of blind decoding trials could be larger if the DCI format is configured by following the legacy system specification.
As specified in Rel. 8-11, the content of the same DCI format can be different for FDD and TDD systems. To be specific, there are additional bit fields in DCI format to support TDD operation. For instance:                In DCI format 0/4 for TDD operation, a 2-bit field is used for UL index or DL assignment index (DAI), but this 2-bit field does not exist in DCI format 0/4 for FDD systems;        In DCI format 1/1A/1B/1D/2/2A/2B/2C for TDD operation, a 2-bit field is used for DL assignment index, but this 2-bit field does not exist in DCI format 1/1A/1B/1D/2/2A/2B/2C for FDD systems;        In DCI format 1/1A/1B/1D/2/2A/2B/2C for TDD operation, a 4-bit field is used for HARQ process number, but there is a 3-bit field in DCI format 1/1A/1B/1D/2/2A/2B/2C for FDD systems.        